Gear device and robot

Abstract

A gear device includes an internal gear, an external gear having flexibility configured to partially mesh with the internal gear and rotate around a rotation axis relatively to the internal gear, and a wave generator configured to come into contact with an inner circumferential surface of the external gear and move a meshing position of the internal gear and the external gear in a circumferential direction around the rotation axis. The external gear includes a cylindrical section including a first end portion with which the wave generator is in contact and a second end portion adjacent to the first end portion along the rotation axis. An inner circumferential surface of the first end portion includes a polished surface. An inner circumferential surface of the second end portion includes a lathe-cut surface.

What is claimed is: 
     
       1. A gear device comprising:
 an internal gear; 
 an external gear having flexibility configured to partially mesh with the internal gear and rotate around a rotation axis relatively to the internal gear; and 
 a wave generator configured to come into contact with an inner circumferential surface of the external gear and move a meshing position of the internal gear and the external gear in a circumferential direction around the rotation axis, wherein 
 the external gear includes a cylindrical section including a first end portion with which the wave generator is in contact and a second end portion adjacent to the first end portion along the rotation axis, 
 an inner circumferential surface of the first end portion includes a polished surface, 
 an inner circumferential surface of the second end portion is an unpolished lathe-cut surface. 
 
     
     
       2. The gear device according to  claim 1 , wherein
 the lathe-cut surface includes a first circumferential groove extending in the circumferential direction around the rotation axis, and 
 the first circumferential groove is formed in a spiral shape. 
 
     
     
       3. The gear device according to  claim 2 , wherein depth of the first circumferential groove is larger in a region separated from the polished surface than a region close to the polished surface on the lathe-cut surface. 
     
     
       4. The gear device according to  claim 2 , wherein depth of the first circumferential groove is smaller in a region separated from the polished surface than a region close to the polished surface on the lathe-cut surface. 
     
     
       5. The gear device according to  claim 1 , wherein the polished surface includes a second circumferential groove extending in the circumferential direction around the rotation axis. 
     
     
       6. The gear device according to  claim 1 , wherein
 the external gear includes external teeth provided at the first end portion, and 
 length of the polished surface in an axial direction of the rotation axis is larger than length of the external teeth in the axial direction. 
 
     
     
       7. A robot comprising:
 a first member; 
 a second member configured to turn with respect to the first member; 
 the gear device according to  claim 1  configured to transmit a driving force for turning the second member relatively to the first member; and 
 a driving source configured to output the driving force to the gear device.